Chronotype, working time and occupational safety: The impact of circadian rhythm and start of working time on sleep duration of employees in the wood and metalworking industry

Abstract

Background and objective: Atypical work times, such as night shifts and very early shifts can have a negative effect on sleep quality and concentration of employees. Sleep disorders are twice as frequent in shift workers as in other workers. Short sleep duration and disturbed sleep are associated with an increased risk of accidents. The purpose of this study was to investigate whether the start of working time and the individual chronotype affect sleep duration. Methods: In a cross-sectional study, 374 employees with a reportable accident at work were asked about their chronotype and normal sleep routine. The employees were chronotyped using the 13-item composite scale of morningness (CSM) questionnaire in the German version. The middle point of sleep was calculated from sleep onset and time of waking up on free days. The effects of shift work, chronotype and age on sleep duration were assessed with multivariable linear or logistic regression. Results: The mean sleep duration without shift work (day work, DW) was 7.2 h (SD 0.9 h). Working early shifts (ES) shortened the sleep duration to 6.4 h (SD 0.6 h). An early start to work is a risk factor for short sleep duration ('7 h) before ES odds ratio, OR = 13.8 (95% confidence interval, CI 3.38–56.25), compared to a late start of working time (evening shift). Being an evening type is also a risk factor for short sleep duration on working days OR = 2.7 (95% CI 0.97–7.67). On days off morning types have a significantly shorter sleep duration than intermediate types OR = 2.2 (95% CI 1.16–4.31). Discussion: A later and more flexible start to work adapted to the chronotype could attenuate the sleep deficit on working days. Working hours that enable a sufficiently long sleeping time and information on health-promoting sleep could contribute to the prevention of fatigue-related accidents at work.